RESUMO
ObjectiveTo investigate the effect of curcumin on the cycle arrest of human colon cancer HCT116 cells and decipher the possible molecular mechanism. MethodThe methyl thiazolyl tetrazolium （MTT） method was employed to examine the effects of curcumin （0， 12.5， 25， 50， 75， 100 μmol·L-1） and 5-fluorouracil （5-FU， 600 μmol·L-1） on the proliferation of HCT116 cells at different time points （24， 48， 72 h）. Flow cytometry was employed to examine the cycle of HCT116 cells treated with curcumin （0， 25， 50， 75 μmol·L-1） and 5-FU. Western blot was employed to determine the expression of proteins in the Janus kinase 1 （JAK1）/signal transducer and activator of transcription 1 （STAT1） /cyclin-dependent kinase inhibitor 1A （p21） pathway in HCT116 cells. The binding of STAT1 to p21 promoter region was detected by chromatin immunoprecipitation （ChIP）. Small interfering RNA （siRNA） was employed to measure the role of STAT1 in regulating the expression of p21 and that of JAK1 in regulating the activation of STAT1 by Western blot and cellular immunofluorescence， respectively. ResultCompared with the blank group， the HCT-116 cells treated with curcumin and 5-FU showed decreased viability （P<0.05）， increased proportions of cells in the G0/G1 phase （P<0.05）， decreased proportions of cells in the S phase and G2/M phase （P<0.05）， down-regulated protein level of phosphorylated p21 （P<0.05）， and up-regulated protein level of p21 （P<0.05）. Compared with the curcumin group， the p21 siRNA+ curcumin group presented decreased proportion of cells in G0/G1 phase （P<0.05）. Compared with the blank group， curcumin elevated the level of phosphorylated STAT1 （p-STAT1） （P<0.05）. Compared with the curcumin group， the curcumin + STAT1 siRNA group showcased up-regulated protein level of p21 in HCT116 cells （P<0.05）. The mechanism study showed that curcumin treatment enhanced the enrichment of STAT1 in the p21 promoter region （P<0.05） compared with the blank group. Compared with the blank group， curcumin up-regulated the level of phosphorylated JAK1 （p-JAK1） （P <0.05）. Compared with the curcumin group， the curcumin + STAT1 siRNA group demonstrated up-regulated protein levels of p-STAT1 and p21 in HCT116 cells （P<0.05）. ConclusionCurcumin may induce the cycle arrest of human colon cancer HCT116 cells by activating the JAK1/STAT1/p21 signaling pathway.